1. Field of the Invention
The subject of this invention is a system for converting the solar energy contained in the surface layers of bodies of water and the kinetic energy of natural gases into electricity using already existing oil drilling platforms as supportive and working bases. The system uses as its working fluid the light hydrocarbon gases extracted by the drilling equipment. These gases are cooled by adiabatic expansion as it does electricity-producing work and reheated by solar energy contained in the surface waters to do more. Electricity produced by the system is transmitted to shore by electric cables supported by pipelines conventionally installed to convey gases and crude oil. Accordingly, the system of the invention affords major capital expenditure savings as compared with the costs of building facilities installed specifically for solar energy recovery.
2. Description of the Prior Art
The prior art to which this invention relates is aware, inter alia, of the early research of D'Arsonval, Georges Claude and of other engineering systems for the low cost production of electricity by the work potential created by the temperature differential between warm and cold layers of water, as set forth in U.S. Pat. Nos: 2,006,985; 2,595,164; 3,321,054 and 3,805,515 to list but a few. If one realizes that about 3600 .times. 10.sup.18 BTU's of energy per year in the form of sunlight reach the earth and about 45 percent of that energy goes to heat the surface layers of the oceans, the potential in this resource becomes obvious. However, the various proposals made in the prior art have not produced ocean thermal energy conversion systems capable of providing electricity at a cost per kilowatt lower than even the presently expensive fossile fuel systems. One main reason for this failure of the solar energy recovery systems to compete with the fossile fuel systems is the high capital expenditure required in building such systems. This expenditure is considerably reduced by the system of the present invention which is built-in or retrofitted on drilling platforms.
As a background to the invention, it should be noted that in the composition of high pressure natural gas drawn from the earth by way of a well or similar tapping means, a mixture of several gases is usually included. The well effluent is normally choked to a reduced pressure and heated to prevent hydrate formation as a result of reduced temperature due to pressure reduction. Thereafter the gas stream is directed through a phase separator, with the gaseous phase carried by way of a pipe line to a storage area, refinery, or other point of utilization.
Such well head effluent as a rule comprises a relatively large methane portion together with fractions of various heavier hydrocarbon gases, as well as water vapor. Normally, the separated gas stream is maintained in the vapor phase due to the high effluent temperature. However, as the gaseous stream is conducted to the point of delivery, a proportion of the effluent, particularly water vapor and higher hydrocarbon fractions will condense in the transmission lines, pumps, valves and other ancillary equipment.
Such condensate is detrimental and must be accounted for, usually by removal, to assure sufficient passage of the gaseous stream. Further, the well head effluent, although comprising essentially methane, always embodies a proportion of light hydrocarbon condensible constituents.
Natural gas mixtures as withdrawn from the earth, vary in composition from one geographical location to another. However, a representative gas mixture include primarily around 60% of methane (CH.sub.4), with amounts of nitrogen and higher paraffins such as ethane (C.sub.2 H.sub.6), propane, butane and heaving including some portion of very high boiling point material normally termed "condensate" (C.sub.10 and heavier). All of these compositions, together with water vapor are found in natural gas in varying amounts.